Driver assistance systems are used to assist the driver in certain driving situations. A driver assistance system may include, for example, an ABS (antilock system), ESP (electronic stability program), a distance-regulating cruise controller (“adaptive cruise control”, ACC), and/or a parking assistant for assisting parking or unparking (leaving a parking space). For at least some of the driver assistance subsystems, determining a vehicle ego-motion is also required. This is so, for instance, in a system for collision-warning, which is based on a prediction as to whether, in response to the continuation of the instantaneous vehicle motion, a collision will occur or not. Parking assistants require data for the instantaneous actual vehicle position with regard to objects bordering on a parking space, for example, for the calculation, monitoring and possibly an adjustment of a trajectory. Parking garage assistants, which include, as a rule, both a collision warning and a trajectory computation, therefore also need information on ego-motion from which an instantaneous position of the vehicle may also be computed.
It is generally known that one may determine a vehicle's ego-motion (self-movement) based on sensors which measure a vehicle state independent of the surroundings. For example, bicycle system sensors, engine system sensors or braking system sensors supply data on vehicle speed, steering sensors supply data on an instantaneous steering angle. In addition, it is also known that one may raise an instantaneous vehicle position based on GPS (“global positioning system”). Data on cornering of the vehicle may be raised possibly based on a gyroscope.
In German Published Patent Application No. 10 2008 036 009, a method is described for protecting a vehicle from a collision in a parking and maneuvering area. For this purpose, ultrasonic sensors record data on the surroundings of the vehicle. From additional data on vehicle speed and the instantaneous steering angle, the ultrasonic sensor data measured in a coordinate system oriented relative to the vehicle are transformed into a coordinate system oriented relative to space, which yields a surroundings map oriented relative to space. From the surroundings map and the ego-motion of the vehicle, a collision probability is calculated of the vehicle with objects located in the surroundings of the vehicle.
From German Patent No. 60 2004 012 962, a method is known for real-time obstacle detection from a vehicle moving relative to a road. Based on images of a video camera, the motion flows of points are calculated whose projected motion is recorded by the camera. Points which belong to potential obstacles, which do not move in common with the plane of the road, are determined via an optical flow method. This camera-based obstacle detection method is able to be combined with additional systems, such as an ultrasonic obstacle detection system, in order to arrive at a greater accuracy and/or a more robust method.
The methods for collision protection and obstacle detection described above are either not very accurate or they are complex. However, if the complexity of a parking assistant, for example, is to remain limited for reasons of cost, this can only be achieved in that, for example, in the calculation of a parking trajectory or for collision warning, comparatively large safety distances are provided. This, however, limits the utility of corresponding systems during assisted parking or during navigation in an unclear surroundings such as a parking garage.